If I disable (false) in the about:config, the error in FireFox turns into "Your connection is not secure" "This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox may only connect to it securely. As a result, it is not possible to add an exception for this certificate." etc.

With Method 2 disabled, I go through Method 1 again and the error becomes "The proxy server is refusing connections" "Firefox is configured to use a proxy server that is refusing connections." etc.